1. Field of the Invention
The present invention is related to the field of detonators for high explosive devices. More particularly, the present invention is related to the field of firing circuits, or activating devices, for safely initiating exploding bridgewire (EBW) detonators.
2. Description of the Related Art
EBW detonators are used to initiate chemical high-explosive devices. EBW detonators provide a substantial improvement in safety when compared with conventional electrically-activated detonators. EBW detonators are insensitive to mechanical impact and are immune to accidental firing caused by spurious electromagnetic (EM) radiation and stray voltages. Sources of spurious EM radiation and stray voltages can include electrical equipment such as radios, arc welding devices, electric motors and power lines.
An EBW detonator is typically activated by a specialized firing circuit, which should be capable of discharging a detonating current of about 1500 volts and 800 amperes in a time of about 1 microsecond. Generally, EBW firing circuits are activated by a power source having a much lower average voltage and current than the detonating current. The lower voltage power source typically charges a capacitor, or other similar energy storage device over a relatively long time period, such as five to fifteen seconds. The capacitor is then rapidly discharged through the EBW detonator when the voltage reaches a predetermined threshold, thereby generating the detonating current.
While the EBW detonator itself is relatively immune to accidental initiation by spurious EM radiation and stray voltages, the firing circuit also must be substantially immune to unintended activation by spurious EM radiation and stray voltage in order to realize the safety benefit of the EBW detonator.
One of the applications for EBW detonators is for initiating oil well perforating guns. EBW detonators are desirable for use in oil well perforating guns because a typical oil well has many nearby sources of spurious EM radiation. Safety of personnel at the oil well would require shut down of electrical equipment and telecommunications equipment near the oil well if conventional detonators were used. This can be expensive and inconvenient, particularly at offshore oil wells.
It is an object of the present invention to provide a firing circuit for EBW detonators which is insensitive to accidental initiation by spurious EM radiation or accidental application of stray electrical voltage to the detonating cable.
It is another object of the present invention to provide a firing circuit which can be used to individually activate more than two separate EBW detonators in an assembly comprising a plurality of EBW detonators.